1. Field of the Invention
The present invention relates to a multi-block copolymer, its producing method and an electrolyte membrane using the same. More particularly, the present invention relates to a branched multi-block copolymer that can be used as an electrolyte membrane of fuel cells applicable to distributed power generation systems, steam supply and power generation systems, power sources of zero emission vehicles, power sources for business, power sources for domestic applications, power sources for mobile devices and so on, and its producing method, an electrolyte membrane made from said copolymer and a fuel cell comprising said electrolyte membrane.
2. Description of the Related Art
Recently, it is expected that conventional energy sources such as oil or charcoal will be exhausted, and thus interests in alternative energy are increasing. Among alternative energy, a fuel cell has high efficiency and abundant energy sources and does not cause emission of pollutants such as Nox, SOx and so on, and thus it becomes the object of attention.
The fuel cell is an electricity generation system for converting energy in a chemical reaction between a fuel and an oxidant into electrical energy. Typically, the fuel cell uses hydrocarbon including hydrogen, methanol, butane and so on as a fuel, and oxygen as an oxidant.
In the fuel cell, a membrane electrode assembly (MEA) is a basic unit for generating electricity. The MEA includes an electrolyte membrane, and an anode and a cathode formed on the opposite side of the electrolyte membrane. The principles of electricity generation in a fuel cell is represented as the following reaction formula 1. Referring to reaction formula 1 (in the case of a fuel cell using hydrogen), oxidation of a fuel occurs at an anode to create hydrogen ions and electrons. The hydrogen ions and electrons move to a cathode through an electrolyte membrane. In the cathode, the hydrogen ions and electrons transmitted through the electrolyte membrane react with oxygen (oxidant) to produce water. The electrons also move to an external circuit.Anode: H2→2H++2e−Cathode: 1/2O2+2H++2e−→H2OEntire: H2+1/2O2→H2O  [Reaction formula 1]
A polymer electrolyte membrane fuel cell (PEMFC) is a type of fuel cell having good energy efficiency, high current density and output density, short operating time and rapid response characteristics to changes in load. An electrolyte membrane of the PEMFC should have high hydrogen ion conductivity, chemical stability and thermal stability at an operating temperature, low gas permeattivity, and in particular, excellent mechanical strength as a separator. In addition to the above-mentioned requirements, the electrolyte membrane needs a manufacturing method of competitive price and environmental friendliness for commercialization.
A fluorine-based electrolyte material, for example, Nafion made by Du Pont, Dow Membrane, Aciplex made by Asahi Chemical and so on, has the reduced hydrogen ion conductivity at a low-humidity and high-temperature process and high production cost. To solve this problem, studies have been made on a nonfluorine-based polymer containing a heat-resistant polymer backbone and a polar functional group attached to the backbone for giving a function as a polymer electrolyte. Of the nonfluorine-based polymer, a poly(arylene ether)-based polymer has an aromatic derivative and an ether bond, and thus it is resistant to heat and chemicals and has excellent mechanical strength and durability and low production cost.
Dimensional stability is one of important characteristics for a polymer electrolyte membrane of a fuel cell because the fuel cell produces a great amount of water, however, so far, any teaching did not disclose a nonfluorine-based polymer electrolyte membrane having advanced dimensional stability.